option to wait for pid file to appear

[igor@xxxxxxxx (Igor Bukanov)]

On 7 June 2018 at 10:35, Lennart Poettering <lennart at poettering.net> wrote:
> Nah, daemon() does not write PID files, you have to do that in your
> own code.

As daemon() calls _exit() (not even exit()) in the parent after the
fork, the only way to synchronize the pid writing is not to use the
daemon() at all and inline daemon() functionality. I doubt that it
will ever be done for the wast majority of sources using the function.
And under systemd there are zero incentives to do that as the
workaround with waiting for the pid file to appear is good enough to
make things reliable. So as such the warning that currently systemd
produces is just a distraction that a user cannot do nothing about.

As a side note the usage of daemon() in 3 from 4 sources I randomly
picked up on github is wrong as the code calls the function and then
writes the pid file right after parsing the config before any
initialization of sockets, but that just pointed out how lack of
simple service initialization API lead to everybody inventing own
buggy code...